Method and means for pre-sealing wood surfaces



UIIit 3,099,695 METHQD AND MEANS FOR PRE-SEALING WOOD SURFACES George Otto Orth, in, Seattle, Wash, assignor to Buifelen Sales Co. Inc., Tacoma, Wash, a corporation of Washington No Drawing. Filed Aug. 17, 1959, er. No. 833,9:52 4 Claims. (Cl. 117$) This invention relates to a novel method and means of pre-sealing wood veneers, plywood surfaces or any flat wood surface to which a sealer is applied and the surface is subjected to high speed sanding.

It is the principal object of this invention to provide a novel and improved method for pre-sealing wood surfaces.

It is a further object of this invention to provide a new and improved surface sealing material which contains substance whereby it is possible to pre-seal the surfaces at a substantially greater speed and at a reduced cost.

Another object of this invention is to provide a surface sealing material which substantially increases the life of the sanding belts.

Still a further object of the invention is to produce an improved and superior pre-sealed surface.

Other objects and advantages of this invention will be readily apparent from the disclosure and detailed description.

A simplified flow diagram of the method is as follows:

Applying the solution to a wood surface Drying the solution to evaporate the organic solvent Sanding the resin and grit coated surface In the past, the pre-sealing of wood surfaces has been accomplished by passing the material through a belt or drum sander and has been at a rate of approximately 16 to 32 lineal feet of material per minute. However, in recent years new techniques and new equipment have made it possible to pre-seal surfaces at a rate of between 50 to 250 lineal feet per minute. In some instances, this is accomplished by a burnishing process such as is taught in the United States patent of Alexander No. 2,827,935. The present invention is not however a burnishing opera tion but a sanding operation. The pro-sealing of material at the substantially increased speed has created many problems. Among other problems, it has found that new and dilferent sealers are required and that the sanding belts must have a greater serviceable life.

The sanding sealers used in the past have included metal stearates, such as zinc, aluminum and so forth in a solu tion of lacquer or resin binders which are so formulated as to be easily sanded down because of their brittleness and lack of thermoplasticity. Such sealers are not satisfactory for high speed sanding and are not economical for use with the present, expensive paper sanding belts. Heretofore it has not been practical to use thermoplastic sealers of low melting point because the sealer will quickly load the sandpaper and destroy its useful life due to the melting of the sealer incident to the heat of a high speed sanding operation. Furthermore, the paper, when loaded, causes defects in the surface due to the tearing effect of the loaded paper.

3,090,695 Patented May 21, 1963 A satisfactory sealer to be used in the present day practice of high speed pre-sealing of wood surfaces must have the ability of producing certain results or benefits. It must make possible longer, effective life of the paper. It must have the characteristics to be readily sanded. The sealer must be capable of taking stain, lacquer, varnish or enamel and yet maintain adequate holdout from the penetration of the coating material. The sealer must not discolor or appreciably stain the wood surface. It must make possible the obtaining of substantially uniform results.

It has been discovered that the desired results and properties can be obtained by using a sealer which includes a dispersed sanding grit, whereby the sealer and grit will build up on the sanding paper or belt so as to continually add to the effective sanding life of the belt. By the use of a sealer containing an abrasive grit, I amable to maintain the sanding characteristic of the belt for a sub stantially greater period of sanding time.

Another important advantage of my improved method of pre-sealing wood surfaces is the uniformity of results obtained during the entire sanding life of the belt. It is believed that it is well known that there is a sharp contrast in the degree and efficiency of a sanding belt between the time of its initial use and after the sanding belt has sanded a few hundred lineal feet. This contrast or difference in sanding efiiciency is materially reduced when employing the method and sealer of my invention. In other words, the effective and eflicient life of the sanding belt is greatly increased so as to produce more uniform results and to reduce the cost of the sanding belts in relation to the quantity of work performed. By various experiments, I have determined that it is possible to obtain a substantial increase in the effective life'of a sanding belt.

Many experiments have been performed in an effort to determine and select a grit or abrasive substance which is most efiicient and satisfactory. Similar experiments have been carried on to select suitable sealers or resins.

I have selected grits or abrasives which will produce a relatively light, or fine build-up on the sanding belt. Materials which I have used include very fine silica, one of which is commercially known as Davidsons Siloid" #152. I have also used diatomaceous earth, powdered glass, white sand, amorphous silica and certain paint pigments extenders. It is to be understood that otherabrasive or grit materials may be used which are capable of being readily dispersed and suspended in a liquid media and which are sufiiciently fine to be applied by conventional methods by a spray device, roll-coater or flowcoater.

The resin sealers which I have used are thermoplastic and are capable of being deposited from solution with very poor solvent cut-back. In other words, the solvent solution of the resin must be capable of originally dispersing the resin and on drying the resin must be insoluble in lacquer or other solvents used in paints and the like. A further requirement of the resin sealer is that it should be somewhat thermoplastic so that as heat is developed by sanding and the friction created between the belt and the treated surface, a portion of the sealer will adhere to the surface of the belt and build up on the belt'. As the build up continues the grit or abrasive is embedded in the accumulated material on the belt and the continuous sandpaper character of the belt is maintained with an equilibrium of sanding loss.

Another requirement of the resin sealer is that it provide-s penetration into the wood being pre-sealed. It is renated alkyd copolymer. I have also obtained satisfactory results with styrenated alkyds but they do not have as much solvent resistance. Polyamid resins work well, especially the high molecular weight Versamids produced by General Mills. Epoxy resins are also satisfactory, however, they are believed to be too costly for present use.

Specific examples of the formulae which I have followed in preparing the resin sealers are as follows:

Example N0. 1

66 lbs. of American Cyanamids Cycopol 320-5, a resin in 50% solution of xylene 4 lbs. of Davidsons Siloid #162, an amorphous silica grinding aid 327 lbs. of toluene The above ingredients will produce 55 gallons of sealer.

Example N0. 2

10 lbs'. of General Mills Versamid 3900 a resin 15 lbs. of butanol solvent 85 lbs. of toluene 1 lb. of diatomaceous earth Other materials may be used as sealers so long as they possess the necessary characteristics. or properties and will provide the proper build-up on the sanding belt.

To determine the optimum quantity or ratio of resin solids and abrasive in the sealer, a series of experiments were conducted. This resulted in a determination that the optimum resin solution is a solution that contains 10% resin solids. The following examples and results show the effect of the variations.

Resin variations:

(1) 20% 320- Cycopol (50% solution) resin solids 1% Davidsons Siloid 162--abrasive 79% toluenesolution 30% 320-5 Cycopol (50% solution) resin solids 1.5% Davidsons Siloid 162-abrasive 68.5% toluene--solution 40% 320-5 Cycopol? (50% solution) resin solids 2% Davidsons Siloid 162-abrasive 58% toluene-solution In the above resin variation it was noted that Example No. 2 produced a spread with low penetration of the sealer into such woods as birch. With poplar-like woods, such as shena, adequate penetration occurred. Satisfactory sanding was obtained on shena and I obtained proper loading of the paper when sanding birch and mahogany. Resin variation No. 3 showed rapid loading of the paper, indicating that there was a low order of penetration and too high a concentration of resin solids on the surface. In contrast, resin variation #1 showed good results with all three species, shena, birch and mahogany. It was thus concluded that the optimum resin ratio appeared to be in the order of resin solids.

A second series of variations were set up using variations in Davidsons Siloid #162. The following examples and results show the effect of the variations.

Abrasive variations:

(1) 20% 320-5 Cycopol (50% solution) resin solids 1% Davidsons Siloid 162 abrasive 79% toluene solution (2) 20% 320-5 Cycopol (50% solution) resi solids 3% Davidsons Siloid #162 abrasive 77% toluene solution (3) 20% 320-5 Cycopol (50% solution) resin solids 5% Davidsons Siloid #162 abrasive 75% toluene solution 4 (4) 20% 320-5 Cycopol (50% solution) resin solids 10% Davidsons Siloid #162 toluene solution Further experiments were conducted using 150 and 200 mesh White sand. In these experiments suspending agents were necessary to hold the sand in solution. In all cases the results indicated the most optimum results were obtained using a ratio of between 5 and 15% abrasive to the resin solids. Thus abrasive variations #1 and #2 showed good results but the panels began to show the effect of whiting slightly with 3% abrasive. Abrasive variations #3 and #4 loaded the paper and showed a white cast on the wood which was undesirable.

Another material which showed promising results as an abrasive was 200 mesh perlite fines which did not settle too rapidly due to the apparent low density. The perlite was used in ratios of 1 to 3% abrasive to the resin solids.

It has been found that sanding belts of a grade or fineness of 7-0 are satisfactory for carrying out the prefinishing in accordance with the teaching of this invention. Coarser paper becomes too brittle in a relatively short period of time due to the stiffness developed from the sealer and abrasive build-up.

It is necessary that the grit or abrasive be relatively fine and that it has the property of remaining suspended in the vehicle or solution. A rapid settling out of the abrasive to the bottom of the container does not permit even distribution on the surface and will not produce uniformity in the presealing of the surfaces. The abrasive must function in a low viscosity and a low total solids vehicle.

Other problems are the absorption character of the abrasive and the adherenceof the resin solids over the abrasive on drying. To meet these problems I found that the abrasive material must be readily suspended in the solution and if the abrasive material does settle out, it must be capable of being resuspended by stirring or agitation.

To obtain the abrasive or grit with the desired properties I have selected those which are capable of being suspended, such as amorphous silicas, and in addition I have added a suspension medium such as collidal silicas or aluminum stearates or calcium stearates.

The stearates alone are not completely satisfactory because they become somewhat gummy. The fine colloidal silicas worked very well but they give th-ixotropy which does not permit rapid penetration into the wood. The lack of proper or adequate penetration is undesirable because it alters the ratio of sealer and abrasive on the surface. Thus, it was necessary to discover a formulation which would produce the desired resultof maximum suspension of the abrasive and holdout.on the surface and also provide ample penetration into the wood. The previously recited formulae give these results.

I have also noted that different species of wood have different absorption rates. Shena or poplar is very absorptive wood and worked exceptionally well in abrasive holdout. In comparison, birch and maple have poor absorption and holdout. This problem was solved by adding thinner and thereby reducing the proportion of total solids. I have found that the ratio of abrasive to resin sealer is important and if there is too much or too little abrasive, it will destroy the equilibrium for the proper deposit and wear-off of the abrasive onto the sanding belt.

If it is desired, color-may be applied to the wood surface simultaneously with the pre-sealing. This is readily accomplished by adding paint pigment or dye to the sealer-abrasive solution. By the selection of the proper V paint pigment or dye it is possible to obtain a translucent,

creased because the grinding or sanding media is replenished on the belt as the surface to be sealed is being sanded. Also a more uniform result is produced so as to produce a superior product at less cost.

In carrying out the method and using the product of this invention, the prepared sealer solution is applied to the wood surface to be sealed. The application may be by hand spraying by the use of a flow-coater or a spraycoater. The rate or quantity of application should be within the range of to 20 pounds of solution per thousand square feet or surface.

After application of the sealer, the sealer is dried by air drying or oven drying. The drying should be sufficient to cause the solvent and suspending media to be evaporated. After sufficient drying has been accomplished, the coated surface is then subjected to high speed sanding at the rate previously mentioned of 50 to 250 lineal feet per minute.

As the sanding continues there is a continual build up and removal of the sealer and abrasive on the sanding belt. The sealer and abrasive which are picked up from the coated surface adhere to the belt but they are continually being removed or ground down as the sanding operation is performed. The optimum situation is achieved when the build up on the belt and the removal from the belt reach an equlibrium wherein the rate of addition and removal is substantially equal.

The preferred sanding medium is at 7-0 sand paper. By following this method and employing and abrasive in the sealer solution, I am able to obtain an extremely smooth, sealed surface. The method can be carried out on a mass production scale and I obtain more uniform results.

What I claim as new is:

l. A method of finishing a surface of wood comprising the steps of providing 10 to 20 units of thermoplastic resin solids having the quality of softening at a temperature produced in the subsequent sanding step, 1 to 10 units of 150-200 mesh sanding grit and to units of organic solvent capable of dissolving the resin, mixing the aforementioned ingredients together to form a sealer solution, applying the sealer solution to the wood surface whereby the sealer solution penetrates into the wood, drying the solution to evaporate the organic solvent, sanding with an abrasive sheet having a grit coated surface of substantially the same fineness as said sanding grit at the rate of SO to 2.50 lineal feet per minute the outer exposed portion of the dried residue of the solution remaining on said wood surface, continuing said sanding step at least until said outer portion of said dried residue becomes soft from friction generated heat and the rate at which said residue is transferred back and forth between said sheet and said surface reaches a state of equilibrium, separating said abrasive sheet from said surface, and allowing the residue to cool and harden on said wood surface.

2. A method as defined in claim 1, wherein said sanding grit comprises amorphous silica.

3. A method as defined in claim 1, wherein said sanding grit includes diatomaceous earth.

4. A method as defined in claim 1, wherein said solution includes a suspension agent of suflicient quality to maintain said grit suspended in said solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,630,395 McCullough et a1 Mar. 3, 1953 2,827,389 Garner Mar. 18, 1958 2,955,958 Brown Oct. 11, 1960 

1. A METHOD OF FINISHING A SURFACE OF WOOD COMPRISING THE STEPS OF PROVIDING 10 TO 20 UNITS OF THEREMOPLASTIC RESIN SOLIDS HAVING THE QUALITY OF SOFFTENING ATT A TEMPERATURE PRODUCED IN THE SUBSEQUENT SANDING STEP, 1 TO 10 UNITS OF 150-200 MESH SANDING GRIT AND 70 TO 90 UNITS OF ORGANIC SOLVENT CAPABLE OF DISSOLVING THE RESIN, MIXING THE AFOREMENTIONED INGREDIENTS TOGETHER TO FORM A SEALER SOLUTION, APPLYING THE SEALER SOLUTION TO THE WOOD SURFACE WHEREBY THE SEALER SOLUTION PENETRATES INTO THE WOOD, DRYING THE SOLUTION TO EVAPORATE THE ORGANIC SOLVENT, SANDING WITH AN ABRASIVE SHEET HAVING A GRIT COATED SURFACE OF SUBSTANTIALLY THE SAME FINENESS AS SAID SANDING GRIT AT THE RATE OF 50 TO 250 LINEAL FEET PER MINUTE THE OTHER EXPOSED PORTTION OF THE DIREC RESIDUE OF THE SOLUTION REMAINING ON SAID WOOD SURFACE, CONTINUING SAID SANDING STEP AT LEAST UNTIL SAID OTHER PORTION OF SAID DIRED RESIDUE BECOMES SOFT FROM FRICTION GENERATED HEAT AND THE RATE AT WHICH SAID RESIDUE IS TRANSFERRED BACK AND FORTH BETWEEN SAID SHEET AND SAID SURFACE REACHES A STATE OF EQUILIBRIUM, SEPARATING SAID ABRASIVE SHEET FROM SAID SURFACE, AND ALLOWING THE RESIDUE TO COOL AND HARDEN ON SAID WOOD SURFACE. 